Every self-respecting author who writes science fiction has tackled time travel at one point in time or another, but this short story by Neatoramanaut Melphistopheles is probably my favorite:

I ran into myself on the bus today. One minute he wasn't there, the next he was. He didn't introduce himself, as I immediately recognized me, and of course he remembered that. I turn out a bit chubbier, and wrinklier with a lot more white hair, but still a lot of red, and still in a ponytail. He had a mechanical hand.

"Still wearing the ponytail." I said.

"Shut up." I replied.

This is going to get confusing, so I'm going to refer to old me as he or him, even though it's actually me.